A Biogeographic History of Mexican and Central American Oaks

Kieran N. Althaus, Marlene Hahn, Silvia Alvarez-Clare, Jeannine Cavender-Bares, Allen J. Coombes, M. Socorro González Elizondo, Antonio González Rodríguez, Paul S. Manos, Hernando Rodríguez Correa, Susana Valencia-A., and Andrew L. Hipp

Published May 2026 in International Oaks No. 37: 233–240

Abstract

Oak trees are among the most diverse and ecologically important groups in North and Central American forests, but we still don’t fully understand how this diversity originated. This is especially true in the mountain forests of Mexico and in Central America, where oaks have undergone remarkable diversification. Using DNA evidence and evolutionary dating methods, we traced the deep history of American oaks back 25 million years. Our results reveal that both major oak sections (Quercus and Lobatae) independently migrated south from the United States into Mexico around the same time, long before the major climate changes that created today’s grasslands and deserts. Rather than being driven by these well-known climate shifts, oak migration appears to have been motivated by the availability of new ecological opportunities in Mexico’s emerging mountain landscapes. Our findings demonstrate that the spectacular oak diversity we see today in Mexico’s mountains has ancient roots, beginning with early migrations that preceded major continental climate changes. This research provides new insights into how mountain ecosystems become biodiversity hotspots, and highlights the role of geographic opportunity in driving evolutionary radiations.

Keywords

biogeography, niche evolution, oak diversity

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